https://www.cnet.com/news/honeywell-home-smart-thermostat-gains-a-room-sensor-ces-2019/

Both Ecobee and Nest already sell temperature sensors that work with their smart thermostats.

The T9 will be available in the spring. Additional room sensors will be sold in packs of two for $80. It will work with Alexa and Google Assistant at launch as well.